Jessica Halliday revels in the history, allure and power of the Christchurch Town Hall's key material: concrete.

It's 2013 and the future of the Christchurch Town Hall is still in the balance. When Kim Hill suggests the Town Hall is a dog, and I'm instantly on the defensive. We're in the middle of a live, face-to-face interview. As for most of us who grew up with the doyenne of New Zealand broadcasting in our ears, informing our understanding of the world, her opinion matters to me – but this time she's prodded an open wound and I toss her words back at her accusingly. Too many significant works of architecture in Christchurch have been demolished since the earthquakes. It's unconscionable to me that we could lose this one.

I have to acknowledge that plenty of people agree with Kim that the Warren and Mahoney-designed building is ugly: a hulking mass of grey concrete that lacks grace and feels oppressive. But for me the Town Hall's concrete is alive with historical resonance and crafted beauty. 

When I was a student, the thing that first made me look differently at concrete in architecture was discovering that to some mid-century architects, exposing concrete wasn't driven by aesthetics; it was about values, about what really matters. In particular, they felt leaving concrete exposed and raw reflected the importance of truthfulness and reality in life and society: it was about seeing, facing and valuing the common and the ordinary. To translate this into architecture required being truthful and honest about what buildings were made of and how they were constructed. 

The concept that architecture could be – and should be – truthful was one the modernists inherited from late 18th and 19th century architects. The notion of truth was used and abused in various ways in the development and history of architectural modernism(s). But it received a huge boost in the early 1950s when Le Corbusier's frank treatment of concrete in the raw (béton brut) in buildings like Unité d'habitation in Marseilles (1947–52) was latched onto by group of young, radical British architects who were known as the New Brutalists.

Originally, The New Brutalism didn't necessitate treating concrete "as found". The major work of architecture that first exhibited the principles of The New Brutalism wasn't even principally made of concrete. The Smithson's Hunstanton School (1950–54) was a Miesian exercise in steel, glass, brick, and some concrete, but without Mies van der Rohe's fine detailing and finishes. But what mattered wasn't the selection of the materials but the "bloody-mindedness" of the approach, meaning a "ruthless … honesty in structure and materials", which at the time shocked an older generation of modernists. To the Smithsons, this rough architectural treatment was "ethical in its deep respect for what is" – in particular, the everyday reality of modern life in the city, especially for the working class.

In 1953 a young New Zealand architect on his OE, Miles Warren, wandered into this London hothouse of architectural debate and energy. Warren got a job working for the London County Council (LCC) architects' office and threw himself into the scene, attending lectures, site visits and taking architectural pilgrimages across Europe. In his own words, he "was extraordinarily fortunate to be sitting right in the middle of the birth of Brutalism. I went over the Hunstanton School with the Smithsons and Ove Arup … lapped up the Corbusian influence of the LCC … and like so many architects, came home to New Zealand brimful of ideas and determined to force them on an unsuspecting public."

Warren's experiences in Europe – working on a public housing scheme of multi-storey towers and blocks using precast and exposed concrete, tours of the continent, and the bloody-mindedness of Hunstanton and the New Brutalists – would influence his approach to architecture for the next 25 years.

Concrete in one form or another became the material of choice for the practice Warren formed with Maurice Mahoney in 1958. Load-bearing concrete block walls (left raw or painted white), precast concrete panels (off the box or finished with a surface of chunky aggregate), concrete structural frames, lintels, steps, oversized railings and upper floors whose soffit (underside) was exposed as a ceiling – all became key elements in the Warren and Mahoney architectural language. The pair were far from alone in this rapid adoption and celebration of a formerly utilitarian material in fine architecture, but in Christchurch they led the way and set the standard.

Warren believed concrete was a natural choice for Christchurch and the South Island – in part because it was a continuation of the brick and stone masonry traditions of the past, and in part because the colder weather demanded a more robust, solid defence against the elements. It was also in contrast to his Auckland-based peers, who had pursued a modernist architecture that drew on a light timber tradition better suited to a warmer climate. Although Warren frequently espoused the "honest use of materials", it became clear that Warren and Mahoney's bold and expressive use of concrete wasn't driven solely by the same values the New Brutalists pursued in their architecture but was also spurred by a conviction that concrete could be used for aesthetic purposes. For while Warren was influenced by his experiences in London and Europe, he'd spent most of his life in Christchurch, soaking up the aesthetic power of Mountfort's Gothic Revival and the Arts and Crafts elegance and refinement of Cecil Wood. 

When the Christchurch Town Hall design competition was announced in 1965, it was a given that the building would be constructed, at least in part, in concrete. By this point in architectural history, modernist architects could no more paint or render over concrete elements than Mountfort would have painted or plastered over the Port Hills stone of his Gothic Revival Canterbury Provincial Council buildings further up the river. 

So much about the Town Hall stems from the sound and spatial qualities that Warren wanted to achieve in the auditorium. These were a sort of holy grail of auditorium architecture in the post-war period: the goal was to design a space which gave every seat good sightlines and proximity to the stage, while having excellent acoustics. This meant solving the acoustical problem of circular or elliptical auditoria. Round concert halls provide good sightlines, intimacy and conviviality but bad acoustics. The conventional shoebox shape used for concert halls provides good acoustics but a poor visual experience for the majority of the audience, who are seated a long way from the stage. 

This historic problem was solved in the design of the Christchurch Town Hall by New Zealand acoustician Sir Harold Marshall. As a result of Marshall's groundbreaking solutions to manage lateral sound reflection in a large circular room, the Christchurch Town Hall has some of the best acoustics of any concert hall in the world while providing the audience with a direct and intimate experience of the performance. This design also creates a special collective atmosphere: before the lights go down, the audience of 2,500 people enjoy a close and social proximity to each other, even from across the room.

Concrete creates the conditions for the building's special acoustics. The two dedicated performance spaces of the Christchurch Town Hall, the auditorium and the James Hay Theatre, need to be acoustically separated from the noisy city they serve. The building's thick concrete walls, floors and ceilings are a means of creating sound-isolated interior spaces. It's incredibly efficient if the materials used for acoustic absorption and separation are also structural. 

The architects' intent to express truth wasn't just in the necessity and reality of materials; it was also to be found in the forms of the building. For Warren, this meant that the required volumes of the interior spaces of the Town Hall determined its exterior shapes. The rather squat and firmly grounded ellipsis of the auditorium sits in contrast to the vertical thrust of the rectangular fly tower of the Town Hall's James Hay Theatre, with its rising fan of seating. The multi-functional Limes Room takes a more anonymous rectangular shape, projecting out over the Ōtākaro Avon River. Suspended below the Limes Room, the restaurant was formed from a tumbling series of linked copper-topped glass boxes, creating a lively atmosphere. All these separate forms are unified by the Town Hall's visible structure in the soaring pairs of concrete columns, cast in situ and left as they were when they were struck "off the box". These columns march around the perimeter of the building, creating a rhythm and pattern of paired elements that carries through into the interior.

As well as being committed to modernism's most infamous dictum – form follows function – Warren valued clarity. Axial planning of the building not only supported his distinct expression of the building's separate functions; it also ensured that circulation was coherent. You recognise the section of the building you're headed for before you even step inside, and beyond the entrance doors, everything is arranged on a clear axis: theatre to the east, auditorium to the west, dining rooms to the south. 

There are lots of ways to express the truth. Concrete is a slurry of cement, water, air, aggregates (gravel, stones) and sand. Poured into formwork or boxing of different shapes, it is usually laid with bars of reinforcing steel to give it the tensile strength it lacks. Formwork can be made from a variety of materials, including timber (boards or plywood sheets), steel, aluminium and plastics. Concrete can be poured in situ, or precast on- or off-site and carted and lifted into position. All of this allows for a multitude of variables, each of which can change the appearance of the finished concrete element and its surface. Architects exploited this variability for aesthetic purposes. They were not just expressing the truth of concrete, but deliberately creating certain visual and tactile effects.

At the time the Christchurch Town Hall was built, the builders, joiners, and workers who mixed and cast concrete were recognised and valued for their craft. They assembled precisely textured formwork, carefully selecting or rejecting timber for its raised grain and swirling knots. The variations of concrete mix were well understood – achieving a particular texture and colour were as important as formulating the correct composition for strength. Knocking it off the box without chips or cracks was an art. It took skill and patience to lay out a surface aggregate to decorate the surface of a precast panel, or to bush-hammer slim vertical ribs to achieve a desired pattern, or to alter a surface finish with acids. Modernist architecture may have celebrated the age of the machine, but it still valued skilfully crafted buildings.

Each of the concrete elements and finishes in the Christchurch Town Hall is carefully considered. The pairs of in situ columns and the chunky beams had formwork of timber boards, whose joinery and surface texture of wood grain and whorls is left legible. In service areas like the kitchen, limited sections of the exterior are finished with a roughcast render, forming a nobbly surface with a uniform colour.  Most of the exterior walls are made from a series of precast concrete panels with an exposed aggregate surface of irregular chunks of stone. These panels are attached onto the concrete walls underneath; while they create a durable finish and no doubt contribute to the sound isolation of the interior, the final finish is an aesthetically driven choice.

It's this bloody-minded, relentless use of concrete that seems to irritate the building's critics. But the concrete finishes have their own visual interest and reward the patient and repeat observer with unexpected delight. There are a wider range of colours on the exterior aggregate than the word "grey" conveys. Here you'll find not just mid and dark greys, but also reddish and brown tones that change with the light and the seasons. On a spring morning from across the Ōtākaro Avon River, the aggregate on the south side of the building is a warm, dark pink, while in the afternoon it takes on cool, blue tones. 

For all its craft, the ordinariness, the "what-it-is-ness" of the Town Hall's concrete exterior is in deliberate contrast with the finer materials and vibrant colour used in the interior. Through the dark, rich, heavy Meranti timber doors, exposed concrete serves as a foil for a white marble floor, bright brass fittings and the rich red fabrics used to line walls and interior doors, carpet the upper floors and upholster the seating. The heaviness of concrete is a counterpoint to the lithe timber members that support the promenade roof on the first floor and the delicacy of the paired balustrades. A close examination of the interior allows you to experience the Christchurch Town Hall as both a spare, modest building (because, let's face it, it's a few fancy dressings on some concrete) and also as rich and complex (boy, there’s a lot going on). Its contradictions make it special.  

Designing contrasting architectural experiences within one building is key to Warren and Mahoney's work, and in the Town Hall this is not just provided by the materials. For example, the sense of compression at the main entrance, where doorways are low, contrasts with and emphasises the vast openness of the interior volume of the auditorium. The clarity of the plan and form of the building, and of the circulation from the foyer into the main performance spaces, contrasts with the layered visual complexity of the mezzanine floors and walkways suspended over and around the foyer. And the riotous colour and joy of Pat Hanly's commissioned painting Rainbow Pieces, visible through the windows, is heightened by the muted grey, brown, pink and blue tones of the exposed concrete that flanks the exterior of the  foyer.

New Zealand very nearly lost this special building. When I lobbied as part of a group of architects and historians to keep the Christchurch Town Hall after the Canterbury earthquakes, our arguments were not based on the heritage value of its primary material – concrete. We emphasised the building's unique place in New Zealand's architectural history, its innovative and acclaimed acoustics and its social and cultural role as the city's living room. However, as the 21st century marches on, we can regard concrete as having new heritage value when we consider it in light of climate change. As well as conserving our existing concrete buildings through maintenance, restoration and retrofitting, we must now ensure that concrete becomes a less frequently used material in new buildings. Thanks to lime-based cement, concrete produces around 8% of global CO2 emissions. We should turn to alternatives wherever possible, especially mass timber. 

Concrete, like other older forms of masonry, should only be selected when there are no viable alternatives; perhaps, like tropical hardwood timbers, its use will become unconscionable. In the future, the concrete of the past may become increasingly valued for its rarity, not just its aesthetics and history. This is the truth about concrete that matters now.

This story was created in paid partnership with The Spinoff. 
The Single Object is a writing series exploring our material culture.

Dr Jessica Halliday is an architectural historian based in Christchurch.